Matricaria discoidea, commonly known as pineappleweed, wild chamomile, disc mayweed, and rayless mayweed, is an annual plant native to North America, northern Asia, and Europe where it grows as a common herb of fields, gardens, and roadsides. It is in the daisy family Asteraceae. When crushed, the flowers and foliage emit a strong pineapple-like aroma, giving the plant its common name. . Each plant typically carries at least five capitula, and each capitulum measures 5–15 mm across. The hollow, conical receptacle contains numerous tubular, bisexual disc florets, each with five stamens and a pistil formed from two fused carpels. As an annual species, the leaves senesce along with the rest of the plant at the end of each growing season.

Microscopically, the leaves are amphistomatic, with stomata present on both the adaxial and abaxial surfaces, positioned close to the epidermis and flanked by oval-shaped guard cells

M. discoidea has a shallow root system defined by a short, thick taproot with many fine secondary fibrous roots. However, there is disagreement over whether it originated in North America or in Siberia. This species has been introduced to Europe, Asia, Iceland, South America, and New Zealand and is now widespread and naturalized in Britain, where it has become one of the fastest-spreading plants of the 20th century.

Reproduction

thumb|Aboveground plant body of Matricaria discoidea.

M. discoidea reproduces solely through seed formation. The flower heads produce small, light brown, ribbed seeds measuring 1.3–1.6 mm in length by <0.7 mm in width and weighing 0.14 mg on average. Each seed is enveloped in a 19.6-22.8 μm-thick seed coat and packaged in a small, dry, indehiscent fruit achene. Shorter photoperiods and later-season germination extend the time to flowering, often causing overwintering as a rosette before blooming the following spring. The main plant has been observed to produce up to six thousand seeds in the United Kingdom, while in Alaska the main plant usually contains 11-1000 seeds. and the species typically produces seeds one or more times per year.

The roots of pineapple weed are colonized by arbuscular mycorrhizal fungi. These mycorrhizae give the plant greater access to water as well as nutrients like phosphorus, nitrogen, sulfur, and trace elements. Its pollen has been identified in brood cells of Megachile versicolor (leafcutter bee).

Uses

The greens can be washed and eaten, and both the flowers and the whole plant can be steeped to make tea, described as "excellent" by one field guide. They have also been used in salads (although they may become bitter by the time the plant blooms). Extracts from the flowers and other aerial parts of the plant have been shown to possess non-toxic, pain-relieving, and mildly sedative effects, reflecting the biological activity concentrated in the floral tissues.

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File:Matricaria discoidea 2637.JPG|The pinnately dissected leaves are sweet-scented when crushed

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File:Pineapple Mayweed (Chamomilla suaveolens) - geograph.org.uk - 497544.jpg

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References

  • USDA Plants Profile for Matricaria discoidea (Disc mayweed, Pineapple weed)
  • Jepson Manual treatment: for Chamomilla suaveolens —Matricaria discoidea
  • University of Michigan Native American Ethnobotany — Matricaria discoidea
  • Pineapple weed - Matricaria discoidea
  • Robbins, W. W., Margaret K. Bellue, and Walter S. Ball. 1970. Weeds of California. Documents and Publications, Sacramento. 547 p.
  • Gregory L. Tilford. 1997. Edible and Medicinal Plants of the West. Mountain Press Publishing Company, Missoula. 110 p.
  • University of California-Davis, Statewide Integrated Pest Management Program — 'Pineapple weed'